This invention relates in general to the audio output of a receiver. More particularly, the invention relates to an apparatus and method for maintaining a substantially level audio output and controlling the tone of the audio output in an audio or audio-visual system.
Examples of audio and/or visual systems include: radios, televisions, tape players, digital tape players, compact disc (CD) players, and digital video disc (DVD) players. Examples of televisions include: analog NTSC television receivers, digital TV receivers or advanced television receivers, and the like. The present invention may also be incorporated in audio encoding or decoder devices.
The loudness of the audio output from a television receiver often changes from program to commercial on a given channel, from program to program on a given channel, and from channel to channel. Additionally, many television programs and most motion pictures intentionally vary the loudness from scene to scene to simulate how the sounds would be experienced in real life. For example, the sound of a gun shot or a cheering crowd at a football game is louder than the sound of two people having a face-to-face conversation in a room.
However, such real life loudness variations, while having some value in a movie theater, are often a source of annoyance when viewing a television program at a relatively close range in a relatively confined area. In an effort to correct this annoyance, some television manufacturers have incorporated automatic volume leveling (AVL) circuitry in their televisions. Such AVL circuits are similar to analog leveling circuitry found in various audio products such as tape recorders. While these analog AVL circuits provide some relief from loudness variations, they generally suffer from having a limited volume hold time for quiet passages, and slow attach and decay (release) times constants. In addition, the AVL circuitry raises the cost of the television.
In addition, the level of loudness perceived by humans varies considerably depending on the frequency and amplitude of the sound. When comparing music in a concert hall with music in a home environment, the music will not sound the same to the listener, even though the frequency spectrum is exactly the same but at a different sound or amplitude level. In particular, the ear is less sensitive to low and high frequencies at low sound levels. This justifies increasing the bass-treble settings for musical sources in the home setting.
Certain conventional systems may have sound equalizers built in for adjusting the bass-treble controls of the system. For listening to the musical contents with conventional systems, the bass-treble settings may be increased to make the music contents sound more realistic. However, for vocal contents, a decrease in the bass and treble settings results in a better signal to noise ratio. An automatic equalizer device alters the source frequency spectrum by automatically adjusting the bass-treble settings depending on the program source.
Accordingly, it would be advantageous to provide an automatic audio leveling and source frequency spectrum equalizing apparatus and method that would provide an infinite hold time for quiet passages, fast and precise attack and decay times, and frequency spectrum adjustments, which would not require additional circuitry.